The mystery over the Israeli bombing of Syrian territory last year took a new twist yesterday when US intelligence agencies showed a video claiming to prove that the target was a covert nuclear plant being built with North Korean help. The White House described the alleged reactor as "a dangerous and potentially destabilising development for the region and the world".

After seven months of silence and evasion from the Bush administration, the CIA director, Michael Hayden, briefed members of the Senate and House armed services, intelligence and foreign affairs committees, saying his weapons specialists found the evidence compelling.

After the Israeli attack last September, there had been speculation that the target was a nuclear reactor but this the first time there has been an official statement, complete with details, and the first time that North Korea has been implicated.

The Bush administration also disclosed that Israel had consulted Washington before launching the strike.

The White House spokeswoman, Dana Perino, speaking after the Senate and House of Representatives had been briefed, said Syria had built the plant "carefully hidden from view" in a remote desert area in the east of the country, in breach of its international obligations.

"We are convinced, based on a variety of information, that North Korea assisted Syria's covert nuclear activities. We have good reason to believe that the reactor, which was damaged beyond repair on September 6 of last year, was not intended for peaceful purposes," she said.

The White House added that the regime moved quickly to bury evidence of its existence, covering over the wreckage and constructing a new building on the site.

US officials said yesterday the Bush administration was putting the information out in order to clear the decks before doing a deal with North Korea to dismantle its nuclear programme.

The video, made public last night after Congress had been briefed, is a collection of material from various sources, in addition to Israeli intelligence. There is no tape from inside the alleged reactor, only two still photographs, apparently taken by a human hand on the ground rather than a drone or satellite. This was supported by satellite pictures and graphs.

The pictures taken on the ground show an apparently empty brown-grey, solid building, but nothing that seems to indicate it is being used for nuclear purposes.

In the video, which shows the site before and after the bombing, the CIA claims that the alleged reactor is similar to one in Yongbyon, 55 miles north of the North Korean capital, Pyongyang.

One official said the Syrian plant was within weeks or months of being operational. "This thing was good to go," he said. Congress was told that the reactor was designed to produce a small amount of plutonium, which can be used to build a nuclear bomb.

In releasing the video, the Bush administration is taking the risk that the North Korea regime may use it as an excuse to walk out of US-North Korean negotiations about dismantling its nuclear programme, but is banking on any such walkout as being only temporary.

Under a deal agreed last year between North Korea, the US, China, Japan, South Korea and Russia, Pyongyang is required to detail whether it has provided nuclear help to Syria and other countries round the world. So far it has failed to deliver.

A US official who had seen the video said: "We cannot move forward [on a deal with North Korea] unless you acknowledge we are doing this with our eyes wide open. And we are going ahead with our eyes wide open."

The Syrian government yesterday denied it had been building a nuclear reactor with North Korean help. Syria's ambassador to Britain, Sami al-Khiyami, described the video as ridiculous: "Unfortunately the scenario of taking and retaking pictures looks like what happened before the Iraq war, when the US administration was trying to convince the world that Iraq had nuclear weapons."

In the run-up to the invasion of Iraq, the Bush administration showed photographs and other material to the UN security council that it claimed amounted to evidence of Saddam Hussein's pursuit of weapons of mass destruction, but which were subsequently proven to be false.

Joseph Cirincione, an expert on nuclear proliferation and head of the Washington-based Ploughshares Fund, said: "We should learn first from the past and be very cautious about any intelligence from the US about other country's weapons."

He insisted there had been no justification for Israeli launching the strike on another country, given there was no imminent danger. He added that Syria was a sideshow that should not deflect attention from the bigger prize of North Korea dismantling its nuclear programme. "The administration is trying to clear up old business, so it does not get in the way of an agreement with North Korea."

The Israeli strike destroyed a large building in the desert near the village of At Tibnah in the Dayr az Zawr region, 90 miles from the Iraqi border.

The strike was reminiscent of one on the Iraqi reactor at Osirk in 1981. But, unlike the Iraqi strike, the attack on Syria initially remained shrouded in mystery, with Bush and other leaders repeatedly deflecting reporters' questions.

At the time, the British intelligence service, MI6, privately briefed the British government that Syria had been building a nuclear reactor. The British government accepted this as credible.

If Syria had been secretly building a nuclear plant, it would have been in breach of the non-proliferation treaty, which requires Damascus to notify the UN watchdog, the International Atomic Energy Agency, of any such plans.

The US media and some analysts speculated that neo-conservatives in the Bush administration, led by the vice-president, Dick Cheney, wanted the North Korea-Syria link publicised to try to wreck the prospect of a deal and to undermine the state department official leading the negotiations, Christopher Hill, the assistant secretary of state for Asia

But US officials, as well as analysts, discounted this, saying the neo-conservatives had been discredited and that pragmatists such as the secretary of state, Condoleezza Rice, who favours a deal with North Korea, remained in the ascendancy.

Backstory

Israel is the sole nuclear power in the Middle East, though it publicly refuses to acknowledge this, and is intent on remaining so. It carried out a pre-emptive air strike against Saddam Hussein's nuclear plant at Osirk in 1981, from which the dictator's nuclear ambitions never recovered, and hinted at similar strikes against Iran, saying it will not allow Tehran to acquire a nuclear weapon.

It was against this background that Israel bombed the alleged Syrian nuclear plant in September. It came as a surprise, given that there had been no speculation that Damascus had been engaged in any such programme. The Israeli prime minister, Ehud Olmert, imposed a news blackout and George Bush also refused at White House press conferences to confirm whether the target was a suspect nuclear plant, until yesterday. At the time, there were questions over why Israel should strike against Syria at such an early stage. One theory was that it was meant as a signal to Iran that if it continued to pursue uranium enrichment, a process that could lead to a nuclear bomb, Israel would bomb its nuclear sites.